Add tests for hook point add hook

[anthonyduong9]

Description

Adds tests for HookPoint.add_hook(). This makes it safer to change the method. @VasilGeorgiev39 wrote a bug while refactoring the method, and it wasn't caught by tests.

Fixes # https://github.com/TransformerLensOrg/TransformerLens/issues/540

Type of change

Please delete options that are not relevant.

• [x] Bug fix (non-breaking change which fixes an issue)

Screenshots

Please attach before and after screenshots of the change if applicable.

Checklist:

• [x] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes
• [x] I have not rewritten tests relating to key interfaces which would affect backward compatibility

[bryce13950]

Thank you very much for adding this! I really appreciate it. If you are interested in helping a bit more, I would be very happy to help you find something to do. If you want to improve test coverage then there is a lot to be done there ehttps://transformerlensorg.github.io/TransformerLens/_static/coverage/. The report at the time of writing this is for 1.19, and 2.0 will be put up tomorrow, which will affect it a bit. Regardless, there is a lot of work that needs to be done there. If you want to do something a bit more interesting, then there is always the potential to add support for new models, and a whole bunch of additional things that are in the pipeline. If you are interested, and you need direction, reach out to me on slack. I am on the Open Source Mechanistic Interpretability channel as Bryce Meyer.